318 DAVENPORT ACADEMY OF NATURAL SCIENCES. 



arcus superior (d) which is bent inward and then prolonged down- 

 ward into the columellce (e, e^) which connect with arcus inferior^ and 

 backward at the sides into the costce superiores dextrce et sinstrce (c, c''). 

 These costcf superiores are extended backward until they become united 

 into a broad plate, which joins with the costce inferiores to form the 

 clavus, and from about their middle they each send off a branch 

 {h, h') which connects with the costce inferiores at the radiating points 

 [f,f'). Tlie broad plate formed of the costoe, superiores probably repre- 

 sents a part of the original sternal portion of the head, say for exam- 

 ple the yula; at least it now forms the division between the head and 

 thorax. Two chitinous pieces (g, g') extend from the radiating points 

 {f.f) about three-fourths of the distance toward the center where they 

 appear to join with two other slender chitinous pieces (i,iO Ij'ing on 

 each side of the oesophagus, (I am however not altogether certain that 

 there is a junction). This complicated frame-work serves to sup- 

 port the enlarged conical bases of the four buccal setae (r, r\ t, t'). 

 Each seta consists of a very long and slender tube enlarged at the base 

 wliich forms an elongated apparently hollow cone [conus). In the outer 

 and lower pair of setae the cones are more elongated, more slender, and 

 they are passed through the clavus until they can go no further on account 

 of the enlarged ends. The interior and upper setaj are more rapidly en- 

 larged at their bases and come together a short but quite perceptible 

 distance above the lower or outer setje. They are also more closely 

 united througiiout their entire length,— while the outer pair are easily 

 separated, tliese usually remain together as if but one piece. This fact 

 has caused many persons to believe that there were but three setse. The 

 four setfB evidently form a tube through which tlie sap is absorbed from 

 the tree— once started it is probable tliat the capillary action would be 

 sufficient to draw up the sap, but Dr. Mark has described a distinct 

 sucking apparatus which he observed in Chionaspis.* Extending for- 

 ward from the junction of the inner setae is the oesophagus {I), at its 

 base are two small chitinous pieces [m, m'), and lying within its swollen 

 part [pharynx) is a small chitinous piece (e) the uva of Dr. Mark. The 

 buccal sette after passing through the clavus enter the cavity of the labium 

 in wiiich they are lield in place, possibly by a crescent-shaped chitinous 

 piece (fig. 35,6), and then pass on and out tiirougli the lips at a. The 

 internal part of the labium is peculiarly modified so as to form a thin 

 transparent elastic sack [crumina) within which the setse are withdrawn 

 whenever the insect wishes to change its feeding place, as is always 

 done when the sap ceases from any cause to flow in sufficient quantities 

 to the leaf or limb on which it is settled. In this case the setse are seen 

 to form a large loop lying in the crumina, within the body cavity and 

 extending back as far as the third or fourth abdominal segments. This 

 withdrawing of the set® is probably accomplislied by means of muscles 

 lying within the labial cavity and possibly attached to the crescent- 

 shaped piece before mentioned. 



[ Besides the Kpecics under consideration I have studied more or less carefully corres- 

 ponding mouth parts in Lecanivm, Aspidioius, Psylla, and Cicada, and in all these the struc- 



*Beitrage, etc., pp. 17-18. 



